This invention relates to a method and apparatus to continuously manufacture red lead (Pb.sub.3 O.sub.4) which is a primary material used to produce storage batteries, anti-corrosion paint, glass, etc.
Metal oxide such as red lead is manufactured by a continuous manufacturing apparatus wherein raw metal lead is oxidized in a heated air atmosphere. The important part of the continuous manufacturing apparatus is a rotary kiln having a rotating inner cylinder which is a cylindrical reaction chamber disposed at a slightly slanted horizontal position and is rotated at a low speed.
The raw metal material is continuously supplied from an inlet port of the rotating inner cylinder. The inlet port is provided at the higher end of the cylinder, since the cylinder is slanted horizontally. Since the rotating inner cylinder of the kiln is heated at high temperature by an internal or external heating means, the metal material is oxidized as it gradually proceeds from the inlet port toward an outlet port provided at the other lower end of the cylinder where the oxidized product is continuously retrieved. Both the inlet and outlet of the rotating inner cylinder are conventionally protected by respective hood means.
This apparatus is provided with not only a heating means to oxidize the raw material at high temperature, but a high-volume air supplying means capable of supplying air at a rate thirty times that actually needed for oxidation. The air supplying means is also capable of introducing high-volume local cooling air in order to prevent overheating of the raw material due to excessive heat of reaction.
Conventionally, red lead is manufactured by baking lead monoxide at about 450.degree. C. Lead monoxide is manufactured by oxidizing metal lead powder. Mass production of lead monoxide is performed by using a ballmill or Barton-pot type lead powder manufacturing device where lead powder is air-oxidized. However, the lead monoxide manufactured by this method inevitably contains 10 to 30% unoxidized metal lead powder.
When lead monoxide, containing metal lead powder in such amounts, is turned onto red lead using the above mentioned continuous oxidizing apparatus, the unoxidized lead powder releases large amounts of heat upon oxidization. The yield of red lead in such a situation is extremely low because of the inadequate capability of the apparatus to control this abrupt generation of reaction heat. Therefore, lead monoxide has to be prepared through an independent apparatus wherein remaining metal lead powder is gradually oxidized.